Salinity indicator



May 17, 1938. M. FfKETAY ET AI.

SALINITY INDICATOR Filed sem.` 1o, l195e A-C-UNF.

l. Patented May 17, 1938 PATENT oFFlcE SALINITY INDICATOR Morris Fred Ketay,- Brooklyn, N. Y., and Joel Darwin Peterson, Roselle, N. J., assignors to Bendix Aviation Corporation,

South Bend,

Ind., a. corporation of Delaware Application September 10, 1936, Serial No. 100,216

Claims.

This invention'relates to devices for electrically measuring and indicating the saline content of l iiuids, and more particularly to the electrical circuits employed in salinity indicators of this type.

One of the objects of' the invention is to provide an improved salinity indicating device in which is embodied a novel electric circuit for effecting movement of that element of the device the position of which serves as an indication of the degree of salinity of the uid being tested.

Another object is to provide a new and improved electrical circuit for use in salinity indicators in which a modified form of Wheatstone bridge/is utilized.

A further object is to provide a salinity indicator of the character referred to in which is included improved means for compensating for variations in the temperature of the fluid being tested.

Still another object is to provide an electrical salinity indicating device of improved construction and of greater accuracy than similar instruments hitherto known to the art.

These and other objects of the invention will appear more fully upon consideration of the detailed description of the embodiment of the invention which follows. ciflc Acircuit arrangement has been disclosed and illustrated in the accompanying drawing, it is to be expressly understood that this drawing is for purposes of illustration only and is not to be construed as a definition oi the limits of the invention, reference being had for this latter purpose to the appended claims.

In the drawing, wherein like `reference characters indicate like elements throughout the sev- `eral views:

Fig. 1 is a view of the face of the meter or indicator of a salinity measuring and indicating device embodying the present invention with the fixed and movable coils of the electrical circuit indicated schematically, the positions of the movable coils and indicating pointer corresponding to a fluid of zero salinity;

Fig. 2 is a diagram of the electrical circuit of a salinity indicator constructed in accordance with the invention; y

Fig. 3 is a schematic rearrangement of the circuit diagram of Fig. 2 more clearly illustrating the modified bridge circuit utilized by the present invention;

Fig. 4 isa vector diagram of the electromag- Although only one spe- Fig. 5 is a vector diagram similar to Fig. 4 but illustrating the conditions existing when the uid is (a) of relatively slight salinity and (b) of sufficient salinity to just effect a balancing of the bridge circuit; and

' Fig. 6 is another vector diagram corresponding to a fluid the salinity of which is greater than that required to balance the bridge circuit.

As shown somewhat schematically and dia-- grammatically in Figs. 1, 2 and 3, the salinity measuring and indicating device of the present invention comprises an electrical meter so combined with a modied form of bridge circuit and a salinity cell,as to give an accurate indication of the degree of salinity of the uid being tested in the cell. Since the resistance to current iiow through the salinity cell varies inversely with the temperature of the uid as well as with its salinity, the vindicator circuit also includes means for compensating for variations in the uid temperature.

The meter or indicating portion of the device consists of movable and fixed elements mounted in a suitable casing 9 in such a manner that the position of the movable element at any instant constitutes a clear indication of the salinity of the fluid being tested. As illustrated, the movable element of the meter -comprises a pair of circular coils of wire C1 and C2 mounted with their planes at right angles to one another and having a common diameter, indicated at I0, which serves as their axis of rotation. Coplanar with coil C1, yand xed with respect thereto so as to rotate therewith about axis IIJ, is a suitv to axis I0. As indicated in Fig. 2, eld coils I3 and III are connected in series across the terminals-of the indicator, said terminals in turn being adapted for connection to any suitable source of alternating current. Movable coils C1 and C2 are electrically connected to the electric circuit of the indicator next to be described by three hair springs (not shown) of negligible torque, two of the springs being connected to the ends of the coils while the third spring is connected to the junction therebetween. The relative positions of these three springs are shown in the circuit diagram of Fig. 2 at the points marked I5, I6 and Il.

'I'he elements of the indicator thus far described are combined and electrically connected with a salinity cell and a novel testing circuit in the manner illustrated in Fig.- 2. As shown therein, the cell comprises a suitable container I 8 for the uid to be tested and a pair of electrodes I9 and which are mechanically held in xed and parallel spaced relation and completely immersed in the uid in container I8. If desired, the salinity cell may be mounted in or secured to the indicator casing 9 and suitable connections provided for enabling the fluid to be tested to flow to and from the container I8. One of the electrodes of the cell, electrode I9 in the example illustrated,

is connected .to the same terminal of the indicator as :field coil I 3 while the other electrode 20 is connected to the opposite terminal through two parallel paths, one path including the fixed resistance R1 and the other comprising movable coils Cz and C1 (in series) and a fixed resistance R3 which serves to limit the current through the coils in the event of a short circuit of the electrodes. Connected in parallel with the cell and coil C2 is a calibrated variable resistance 'l' which is adapted to be manually adjusted to correspond to the temperature of the uid being tested in the cell. Another fixed resistance R2 may be shunted across coil C1 and resistance R3 in order to ensure a proper division of current ilow between the coils C1 and C2. As is best illustrated by Fig. 3, the electrical circuit just described is in fact a modlfied form of Wheatstone bridge with the resist-- ance B of the iluid in the cell and temperature compensating resistance T constituting the parallel variable legs of the bridge and the coil C2 functioning as the bridge wire.

Referring now to Fig. 4, let it be assumed that the salinity of the uid under test is zero-that is, the iiuid contains no salt; the resistance of the fluid tothe passage of alternating current then approaches an innite value. Under these circumstances, if the terminals of the indicator be connected to a source of alternating current, the entire current will pass through that leg of the bridge circuit containing the temperature compensating resistance T and then divide between the coils C1 and C2. If at any instant the magnetic elds of lfixed coils I3 and I4 are as represented by the vectors F1a and F14, the circuit is such that the elds of coils C1 and C2 will be represented bythe vectors F1 and F2, as shown. The resultant of the latter two perpendicularly directed elds will be a field represented by the vector R which will attempt to align itself with the main field F13, F14 of the fixed coils I3 and I4. Inasmuch as the coils'Ci and C2 are free to rotate about the axis I0, the tendency to alignment of the resultant and main elds will place the coils C1 and C2 in the positions indicated which, in turn, will carry the pointer II over the scale I2 to the position shown in Fig. 1. When the direction of the current ow is opposite to that just considered, the of Fig. 4 will be reversed; however, since all of the elds of the circuit are reversed, the pointer will remain in the same position. Furthermore,

so long as the salinity of the fluid remains zero, any change in temperature of the fluid or any variation in the resistance T will likewise have no eiect upon thel position of the pointer. While a change in the resistance T will vary the total amount of current passing therethrough and bridge, the

directions of the vectors hence vary the current owing through both coils Ci and C2, the relative amounts of current owing in coils C1 and C2 remain the same With the result that the resultant iield R of said coils, although altered in magnitude, will not be changed in direction and the pointer vII will remain in the position shown in Fig. 1. This xes the zero position of the pointer.

If it now be assumed that the iluid being tested is slightly saline, the resistance to the passage of current between electrodes I9 and 20 is reduced to a finite value. Under these conditions, the current flowing in the circuit passes part through the leg of the bridge containing the resistance T and part through the leg represented by the resistance B, thus tending to balance the bridge and reduce the current through the coil C2. Due to the consequent reduction in the current passing through the resistance T, the current flow through the coil C1 will be slightly increased. The fields of the coils Ci and Cz will then b'e of the magnitude and direction represented by the vecfield will again tend to align itself with the main field of the xed coils I3 and I4, the coils Ci and C2 will be rotated through the angle a, this rotation in turn moving the pointer II through an equal angle in a clockwise direction.

If, at this time, the temperature of the uid in the container I8 should increase, there would result a ldecrease in the cell resistance B and an increase in the amount of current flowing through the corresponding leg of the bridge circuit. However, this temperature change may be manually compensated for by decreasing the variable resistance T suil'iciently to result in the same unbalance of the bridge as before, and therefore the same ratio of field strengths of the coils Ci and C2.

If the salinity of the uid were such that its resistance acted to balance the bridge, the current in coil C2 would be zero and the resultant eld of the coils Ci and Cz would be the eld of the coil Ci. In this case, the coils C1 and C2 would be rotated from their zero positions through the angle b indicated in Fig. 5 to bring the eld Fi of coil C1 into alignment with the main field, the pointer II turning through a like angle from the position shown in Fig. 1. Here again any reduction in fluid resistance due to an increase in temperature would be compensated for by reducing the resistance T sufficiently to rebalance the bridge.

If the salinity of the fluid should increase beyond that suflicient to elfect a balancing of the bridge would again be unbalanced, but in a direction opposite to that previously described, and the field of the coil C2 would be reversed. Under these conditions, the positions of the 'vectors representing the iields of the several coils, after alignment of the resultant eld with that of the fixed coils, would be as shown in Fig. 6. In this case, the pointer II will swing even further in a clockwise direction, as viewed in Fig. 1, onto the right-hand portion of the scale I2.

Anyvreduction in circuit resistance with an increase of 'temperature will still be compensated for by reducing the resistance T to produce the same degree of unbalance of the bridge as before and thereby maintain the correct pointer position.

'I'here is thus provided by the present invention an improved salinity measuring and indicating device embodying a novel electrical circuit for producing an accurate indicatlonof the salinity of the iiuid under test, the said circuit constituting a modied form of Wheatstone bridge and including as one of the variable legs thereof a manually adjustable resistance which serves to compensate for variations in the fluid temperature. Although only one particular form of indicator has been specically disclosed, it will be obvious that the invention is not limited thereto but is capable of a variety of mechanical embodiments. Various changes, which will now suggest themselves to those skilled in the art, may be made in the forni, details of `construction and arrangement of the elements Without departing from the spirit of the invention. Reference is,

therefore, to be had to the appended claims for a deiinition of the limits of the invention.

What is claimed is:

1. In a. salinity measuring and indicating device, a pair of spaced electrodes adapted to be immersed in the fluid the salinity of which is to be determined, a meter for indicating the current flow between said electrodes, comprising mutually interacting iixed and movable coils, a variable resistance calibrated in terms of the temperature of the fluid being tested and manually adjustable to compensate for variations in said temperature and a iixed resistance; said lelectrodes, meter, variable resistance and fixed resistance being electrically connected together in the form of a. Wheatstone bridge with the electrodes and variable resistance lying in parallel legs of the bridge, one of said coils constituting the bridge wire across one diagonal of the bridge, a second coil connected across the other diagonal of the bridge, and a third coil comprising a third leg of the bridge.

2. In a salinity measuring and indicating device, a pair of spaced electrodes adapted to be immersed in the fluid the salinity of which is to be determined, a meter for indicating the current flow between said electrodes including a plurality of iixed coils adapted to produce a main magnetic field, a pair of movable coils mounted in said iield and having a common diameter about which they are free to rotate as an axis and an indicating member xed with respect to said movable coils for rotation therewith about said axis, a variable resistance, and a iixed resistance said electrodes, movable coils and'resistances being electrically connected together in the form of a Wheatstone bridge with the electrodes and variable resistance lying in parallel legs of the bridge and one of said movable coils constituting the bridge wire, the other movable coil and fixed resistance comprising the other two legs of the bridge. I

3. In a salinity measuring and indicating device, a pair oi' spaced electrodes adapted to be immersed in the fluid the salinity of which is to be determined, a meter for indicating the current `iiow between said electrodes including a plurality of fixed coils adapted to produce a main magnetic field, a pair of movable coils mounted in said eld and having `a common diameter about which they are `fi.'i:eetiyrgitate"as an`axis.

and an indicating member iixed with respect to said movable coils for rotation therewith about said axis, a variable resistance, and a xed resistance, said electrodes, movable coils andresistances being electrically connected together in the form of a Wheatstone bridge with the electrodes and variable resistance lying in parallel legs of the bridge and one of said movable coils constituting the bridge Wire, the other movable coil and lxed resistance comprising the other two legs of the bridge, said variable resistance being calibrated in terms of the temperature of the iluid being tested and manually adjustable to compensate for variations in said temperature.

4. In a salinity measuring and indicating device, a pair of spaced electrodes adapted tobe immersed in the fluid the salinity of which is to be determined, a meter for indicating the current flow between said electrodes including a pair of parallel xed coils arranged on a common axis and adapted to produce a main energetic field, a pair of movable coils mounted in said field with their planes at right angles to one another and having a common diameter about vwhich they are free to rotate as an axis and an indicating pointer iixed with respect to said movable coils for rotation therewith about said axis, a variable resistance, and a xed resistance, said electrodes, movable coils and resistances b eing electrically connected together in the form of a Wheatstone bridge with the electrodes and variable resistance lying in parallel legs of the bridge and one of said movable coils constituting the bridge wire, the other movable coil and xed resistance comprising the other two legs of the bridge.

5. In a, salinity measuring and indicating device, a pair of spaced electrodes adapted to be immersed in the iiuid the salinity of which is to be determined, a meter for indicating the current flow between said electrodes including a pair of parallel fixed coils arranged on a common axis and adapted to produce a main magnetic field, a

f pair of movable. coils mounted ,inl said eld with their planes at right angles to one another and having a common diameter about which they are free to rotate as an axis and an indicating pointer xed with respect to said movable coils for rotation therewith about saidaxis, a variable resistance, and three fixed resistances, said electrodes, movable coils and resistances being electrically connected together in the form of a Wheatstone bridge with the electrodes and variable resistance forming two of the parallel legs of the bridge and one of said movable coils constituting the bridge wire, the other movabley coil being connected in series with one of the said fixed resistances to form the thirdv leg of the bridge and the second fixed resistance completing the bridge, the third iixed resistance` being shunted across said third leg of the bridge to ensure a proper division of current betweenl said movable coils.

MORRIS FRED KE'I'AY.

JOEL DABWINPEI'ERSON. 

